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On January 16, 1998, the National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from employees working at the U.S. Postal Service Vehicle Maintenance Facility located in Chicago, Illinois. The request stated that employees were experiencing headaches, sneezing, coughing, unspecified respiratory problems, fatigue, and eye irritation that they believed were caused by exposures to vehicle exhaust. Workers were also concerned about their exposures to paint vapors containing 1,6-hexamethylene diisocyanate (HDI) and about the effectiveness of existing ventilation systems. Site visits were conducted on June 18-19, 1998, and on August 26-28, 1998, consisting of both a medical and industrial hygiene component. A visual inspection was made during the site visit of June 19, 1998, and ventilation measurements were made to evaluate the design and performance of the facility's tail-pipe exhaust systems and roof ventilators. In the facility's repair bay and paint shop a general inspection was made to identify potential safety and health hazards. Personal protective equipment and employee work practices were evaluated. Material safety data sheets, previous industrial hygiene reports, safety training records, and management's written respiratory protection program were reviewed. Air sampling was performed on the visit of August 26-28, 1998, to measure vehicle exhaust components (nitric oxide [NO] and nitrogen dioxide [NO2]) and HDI in the paint shop. Short-term air sampling for NO2 revealed concentrations up to 0.68 parts per million (ppm), below the NIOSH 15 -minute short-term exposure limit of 1 ppm. Full-shift air sampling revealed NO concentrations up to 0.73 ppm, well below the NIOSH recommended exposure limit of 25 ppm as an 8-hour time-weighed average concentration. Air sampling revealed painters' short-term exposures to HDI as high as 692 micrograms per cubic meter (ug/m3), exceeding a Swedish ceiling limit of 200 ug/m3 for HDI-based polyisocyanate and the United Kingdom Health and Safety Executive (UK-HSE) ceiling limit of 70 ug/m3 for total HDI. Painters were exposed to these elevated HDI concentrations while using full-faced air-purifying respirators, rather than using supplied-air respirators as recommended by NIOSH and the paint manufacturer. Qualitative ventilation measurements indicate the two tail- pipe exhaust systems in the repair bay did not meet minimum airflow exhaust criteria recommended by the American Conference of Governmental Industrial Hygienists. The inspection of the tail-pipe exhaust system revealed missing cone hoods, damaged flexible ducts, and inoperative crank-pulley mechanisms. Only two of six roof ventilators serving the repair bay were working during the evaluation. Safety deficiencies were discovered that included the absence of an emergency eyewash near corrosive materials, improper storage of chemical supplies and respirators, and flammable storage cabinets not grounded for fire prevention. The medical evaluation consisted of a walk-through tour of the facility, interviews with eight workers, and a symptom and exposure questionnaire. Symptoms reported in the interviews included asthma, headaches, fatigue, rashes, and eye irritation. A questionnaire was given to 77 workers; workers receiving the questionnaire included mechanics, painters, body shop workers, and office workers, and the areas where they worked included the paint shop, repair bay, and offices. Sixty-two workers (81% of the 77 answering the question) reported smelling diesel exhaust and the relationship to symptoms could not be evaluated because of the small number (5) who reported not smelling diesel exhaust. Forty-six workers (60%) reported smelling vehicle paint vapors when they worked. Smelling vehicle paint was statistically associated with chest tightness (odds ratio [OR]= 7.1, 95% confidence interval [CI] 1.5-34.2), difficulty breathing (OR=4.1, 95% CI 1.0-16.2), irritated eyes (OR=3.9, 95% CI 1.3 -11.2), and morning phlegm (OR=3.7, 95% CI 1.1-12.8).